The present invention relates to a correcting apparatus in a sync signal detector suitable for a satellite broadcasting transmission/reception system format of Korean and European districts for correcting to output original data when 47 sync is phase-shifted by 180.degree. to be provided as B8 sync, and more particularly to a phase shift correcting apparatus of a sync detector in a satellite broadcasting reception system for detecting and correcting a phase shift of 180.degree. during a sync detection of a QPSK (Quadrature Phase Shift Key) signal.
In order to demodulate a QPSK signal in a satellite broadcasting reception system, as shown in FIG. 1, I and Q signals are decoded in a decoder 10, and a sync signal is detected from a sync detector 20. Thus, an error of the I and Q signals being synchronized via a deinterleave circuit 30 with respect to a transport packet is checked. Then, the I and Q signals completely subjected to the error checking are decoded in a Read-Solomon decoder 40 to be restored via a descrambler 50.
Here, conventional sync detector 20 utilized for demodulating the QPSK signal is provided to demodulate the QPSK signal using a unique sync word, of which circuit construction is illustrated in FIG. 2.
As shown in FIG. 2, sync detector 20 according to the conventional technique includes a sync comparator 1 for comparing input data and the sync, and a first sync detecting part 2 for separating to detect sync data from the output data of sync comparator 1. A window comparator 3 compares the sync data in a sync data section from first sync detecting part 2, and a window counter 4 provides a window pulse of the sync section to window comparator 3. A second sync detecting part 5 detects a sync signal from the output signal of window comparator 3, and a sync latch 6 latches the output of second sync detecting part 5 to supply a sync pulse. A serial/parallel converter 7 converts the input data into parallel data, and a data latch 8 latches the data from serial/parallel converter 7 for supplying data stream.
The sync detector constructed as above according to the conventional technique compares the data received in a format as shown in FIG. 3A in sync comparator 1 to separate the sync data as shown in FIG. 3B in first sync detector 2.
The sync data is compared with the pulse as shown in FIG. 3C supplied from window counter 4 in window comparator 3 to be provided to second sync detecting part 5. By doing so, second sync detecting part 5 detects the sync signal as shown in FIG. 3D, thereby producing a sync pulse clock via sync latch 6.
Meantime, the input data is converted to the parallel data in serial/parallel converter 7 to be supplied as the data stream via data latch 8.
However, in the sync detector according to the conventional technique constructed as above is utilized only when demodulating the unique sync word bitstream for preventing the phase shift of 90.degree., 180.degree. and 270.degree. during the reception of the QPSK signal, i.e., the QPSK signal using the transport packet. Consequently, it is not suitable for the satellite broadcasting system of the Korea and European district having different signal (transmitting) format due to the distinction of the areas.
Furthermore, since the descrambler is constructed to be reset when the sync value is BS, the occurrence of the phase shift of 180.degree. in the sync signal serves as a reset of the descrambler whenever the 47 sync data is phase-shifted by 180.degree. to be supplied as B8 sync data. Therefore, the data demodulated to be output is changed as the data which is absolutely different from the original data.